Since vinylidene fluoride base fluororubbers are elastomers with excellent heat resistance, chemical resistance and mechanical strength, they are used in the industry over a wide variety of fields including automobiles and machinery.
However, their chemical resistance is rather insufficient in that they are readily swollen in polar solvents such as ketones, lower alcohols, carbonyl and organic acids, and degraded with amine chemicals, resulting in extraordinary losses of rubber strength and elongation. As to the low-temperature property, fluororubbers lose rubber elasticity at temperatures below −20° C., so that they serve no longer as sealing members. In general, their use in cold latitudes is limited.
For obviating these drawbacks, Japanese Patent Nos. 2990646, 3573191 and 3633836 disclose fluorinated curable compositions of liquid or millable type primarily comprising a perfluoro compound and a fluorinated organohydrogenpolysiloxane. However, molded parts of these fluorinated curable compositions are most often expensive because they are difficult to blend with inexpensive rubber of different species. They are thus limited in use or application.
With respect to rubber physical properties and workability, some other species rubbers are excellent. Specifically, the fluororubbers are surpassed by silicone rubbers in rubber strength, elongation, compression set, roll workability and mold release.
Since the fluorinated curable composition has the prominent features of solvent resistance and chemical resistance, it is sometimes preferred for those articles which are partially contacted with solvents or chemicals that only a contacting portion be made of the fluorinated curable composition and the remaining portion be made of another species rubber.